re: Endothermic Crocs in Nature

[Tim Williams <twilliams_alpha@hotmail.com>]

David Peters wrote:

> <Considering that early crocs are hard to distinguish from early dinos 
> (witness
> Macelognathus, Scleromochlus, etc.), especially when just their bits and 
> pieces
> are known,

To be fair, and as you allude to, the original material for _Macelognathus_ 
was very scrappy.  As Gohlich et al. (2005) say: "_Macelognathus vagans_ was 
described by O.C. Marsh in 1884, based on a mandibular symphysis... New 
material of this species from the Morrison Formation of western Colorado 
demonstrates its affinities with basal crocodylomorphs ..."  Marsh and his 
successors could be forgiven for not knowing the precise identity of 
_Macelognathus_.

_Scleromochlus_ is neither dinosaurian nor crocodylomorph, AFAIK.  Here the 
problem is not so much the lack of material (we have several specimens), but 
the difficulty in discerning characters in these specimens, which are all 
natural casts in coarse-grained sandstone, and very small to boot.  (Not 
that I'm advocating anybody booting lil' _Scleromochlus_ ...)

> As Greg Paul has noted earlier, apparently the easiest
> time for a taxon to revert is when it is only a few steps into the next 
> level.

Greg cites this in support of "neoflightlessness" in early birds.  This 
"rule" makes a great deal of intuitive sense; but I have yet to see any hard 
evidence (e.g., similar reversions of incipient or nascent ecomorphologies 
in other lineages).  For example, I know of no "neoflightless" insects, nor 
"neoamphibious" proto-cetaceans.


Tim